There have been countless attempts throughout the printing industry to apply and control moisture in paper. Attempts have been made in the past to add liquids such as dyes, low-viscosity coatings and moisture to a moving web in such a manner as to control the liquid application along the length and width of the web. Such attempts have consisted of application of atomized particles in the form of mist, steam or spray to the web which results in only partial coverage of the web by the atomized particles or uneven application thereof and lack of adequate control of the amount and density thereof.
Another system used in the past is by means of rolls wherein an uncontrollable quantity of liquid is applied to the web. Various other devices have been used such as scrapers, knives, blades, etc. as the sole means for controlling the thickness of liquid applied to the web from a roll. Such devices are undesirable because it is difficult to adjust flexible blades lengthwise and because the slightest adjustment of the blade may change the film thickness more than is desirable.
Environmental chambers, wherein a moving web is passed through a humid atmosphere within a chamber, have been unsatisfactory because only surface quantities are added to the web due to the limited time of exposure of the web to the humid atmosphere as it passes through the chamber. As a result, the web does not absorb sufficient quantity of the liquid. Furthermore, one side application is virtually impossible. Control of moisture by varying web speed through drying devices or by varying the drying temperatures and humidity is not only difficult but undesirable and costly.
Applying moisture (humidity) and/or coatings to one or both sides of a cut sheet has been previously impossible, or at least impractical, slow, and expensive, particularly where 100% coverage was required. Consequently, systems to date have been limited to application of moisture to a web of material rather than individual sheets.